Re: [PATCH] mm: check nr_initialised with PAGES_PER_SECTION directly in defer_init()

[Wei Yang <richard.weiyang@gmail.com>]

On Thu, Dec 20, 2018 at 03:50:29PM -0800, Alexander Duyck wrote:
>On Thu, 2018-11-22 at 17:48 +0800, Wei Yang wrote:
>> When DEFERRED_STRUCT_PAGE_INIT is configured, only the first section of
>> each node's highest zone is initialized before defer stage.
>> 
>> static_init_pgcnt is used to store the number of pages like this:
>> 
>>     pgdat->static_init_pgcnt = min_t(unsigned long, PAGES_PER_SECTION,
>>                                               pgdat->node_spanned_pages);
>> 
>> because we don't want to overflow zone's range.
>> 
>> But this is not necessary, since defer_init() is called like this:
>> 
>>   memmap_init_zone()
>>     for pfn in [start_pfn, end_pfn)
>>       defer_init(pfn, end_pfn)
>> 
>> In case (pgdat->node_spanned_pages < PAGES_PER_SECTION), the loop would
>> stop before calling defer_init().
>> 
>> BTW, comparing PAGES_PER_SECTION with node_spanned_pages is not correct,
>> since nr_initialised is zone based instead of node based. Even
>> node_spanned_pages is bigger than PAGES_PER_SECTION, its highest zone
>> would have pages less than PAGES_PER_SECTION.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>
>This all seems to make sense to me, and appears to be a valid
>improvement.
>
>Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Thanks :-)

>
>> ---
>>  include/linux/mmzone.h |  2 --
>>  mm/page_alloc.c        | 13 ++++++-------
>>  2 files changed, 6 insertions(+), 9 deletions(-)
>> 
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index ae7a830a21eb..68d7b558924b 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -692,8 +692,6 @@ typedef struct pglist_data {
>>  	 * is the first PFN that needs to be initialised.
>>  	 */
>>  	unsigned long first_deferred_pfn;
>> -	/* Number of non-deferred pages */
>> -	unsigned long static_init_pgcnt;
>>  #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
>>  
>>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 76e12179cd5e..b542d82400cf 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -326,8 +326,13 @@ defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
>>  	/* Always populate low zones for address-constrained allocations */
>>  	if (end_pfn < pgdat_end_pfn(NODE_DATA(nid)))
>>  		return false;
>> +
>> +	/*
>> +	 * We start only with one section of pages, more pages are added as
>> +	 * needed until the rest of deferred pages are initialized.
>> +	 */
>>  	nr_initialised++;
>> -	if ((nr_initialised > NODE_DATA(nid)->static_init_pgcnt) &&
>> +	if ((nr_initialised > PAGES_PER_SECTION) &&
>>  	    (pfn & (PAGES_PER_SECTION - 1)) == 0) {
>>  		NODE_DATA(nid)->first_deferred_pfn = pfn;
>>  		return true;
>> @@ -6451,12 +6456,6 @@ static void __ref alloc_node_mem_map(struct pglist_data *pgdat) { }
>>  #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
>>  static inline void pgdat_set_deferred_range(pg_data_t *pgdat)
>>  {
>> -	/*
>> -	 * We start only with one section of pages, more pages are added as
>> -	 * needed until the rest of deferred pages are initialized.
>> -	 */
>> -	pgdat->static_init_pgcnt = min_t(unsigned long, PAGES_PER_SECTION,
>> -						pgdat->node_spanned_pages);
>>  	pgdat->first_deferred_pfn = ULONG_MAX;
>>  }
>>  #else

-- 
Wei Yang
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